Floh has a good point. What formats do you work in? What codecs do you typically work with or would like to work with? What type of clients do you typically have?
At the end of the day, these things are tools and you are the craftsman.
What computer you decide to run on is your choice too. The new thing is obviously the MAC Pro’s. But remember the G-5 that was the only computer Apple offered a week ago is still as good and fast now as it was then.
You use the Media 100 now, if you like it and wany pretty much the same experience but faster, go with the SDE. If you’d like to move into the HD eventually but not today, then the HDE is the way to go.
Scott F